Chapter 19

Chapter 19 - Chapter 19 (pg 515-536) Intro Regulated genes...

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Chapter 19 (pg 515-536) Intro Regulated genes – genes whose activity is controlled in response to the needs of a cell or organism Constitutive genes (aka housekeeping genes) – genes that are always active in growing cells b/c their products are essential to the normal functioning of a growing and dividing cell, no matter what the conditions are Genes which encode proteins that work together in the cell are usu organized into operons genes are adjacent to each other and are transcribed together onto a polycistronic mRNA regulation of the synthesis of this mRNA depends on interactions btwn regulatory protein and a regulator sequence called an operator The lac Operon of E. coli Intro Inducible: when a gene expression is turned on in a bact by adding a substance (inducer) to the medium induction: producing gene product in response to inducer effector molecules: help control expression of many regulated genes; includes inducers; cause allosteric shifts in repressor proteins to alter affinity for operator sites inducible gene transcribed in response to a regulator event occurring at a specific regulatory DNA sequence adjacent to/near the protein-coding sequence regulatory sequence itself doesn’t code for any product Inducible operon: ex is lac operon Lactose as a Carbon Source for E. coli energy source: glucose metabolism lactose (glucose+galactose) can be substituted if lactose and no glucose enzymes to metab lactose synthesized (genes only active if lactose is present) β -galactosidase: breaks down lact into glucose & galactose; catalyze ismoermation of lactose to allactose (helps regulate expression of lac operon) lactose permease (aka M protein) – in cytoplasmic membrane; transports lact into cell transacetylase coordinate induction: increase of [above Es] in absence of gluc & presence of lact allolactose responsible mRNA for Es have short ½ life transcripts continuously made Experimental Evidence for the Regulation of lac Genes from Jacob & Monod
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Picture 1 Mutations in the Protein-Coding Genes Basics - β -galactosidase gene – lacZ - lactose permease gene - lacY - transacetylase gene – lacA mutations (lacZ-, lacY-, lacA-) used to map genes - tightly linked in order lacZ-lacY-lacA missense mut (bp change in DNA change mRNA etc) affects function of product of gene w/ mutation - nonsense mut (early stop codon) expected to do same - but knocked out functions of all 3 genes when present in lacZ - knocked out only lacY & lacA when present in in lacY same trend in lacA - these 3 different effects said to exhibit polar effects (phenomenon called polarity)
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This note was uploaded on 02/09/2010 for the course BIOL 3301 taught by Professor Hannig/miller during the Spring '10 term at Dallas.

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Chapter 19 - Chapter 19 (pg 515-536) Intro Regulated genes...

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